— Lab’s expertise in accelerator technologies has spiraled out from Ernest Lawrence’s earliest cyclotron to advanced compact accelerators
Lawrence’s invention of the cyclotron in the early 1930s proved to be one of the transformative innovations in modern science. Much the same could be said for the workstyle pioneered at his laboratory: a framework for designing, building, and operating these machines of big science with multidisciplinary teams. Building upon decades of accelerator expertise in a collaborative team-science atmosphere, we are now working on a new generation of innovations in advanced accelerators and their components. Join us for a quick look at some highlights of this rich history and of what the future may hold.
Accelerators have been at the heart of the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) since its inception in 1931, and are still a driving force in the Laboratory’s mission and its R&D program.
Laboratory founder Ernest O. Lawrence invented this first circular particle accelerator. Cyclotrons of all sizes are still used at Berkeley Lab and elsewhere for a wide variety of purposes. They were joined by a succession of new accelerator technologies that continue to enable progress, and the Laboratory’s contributions to state-of-the-art accelerators today — and those of the future — have worldwide benefit throughout the sciences.
“Our work in accelerators and related technologies has shaped the growth and diversification of Berkeley Lab over its long history, and remains a vital core competency today,” said James Symons, associate laboratory director for Berkeley Lab’s Physical Sciences Area.
Cyclotrons and their successors lead to discovery science — and a national laboratory
Dubbed “atom smashers” early on, cyclotrons accelerate charged particles with strong electric fields. Powerful magnetic fields guide the particles in a spiral path as they gain speed and move outward from the device’s center.
This technology catalyzed progress in multiple scientific disciplines. Cyclotrons were used to create different elements by bombarding a target material with a beam of protons, for example, and to explore the structures of atomic nuclei. All in all, Berkeley Lab scientists participated in the discovery of 16 elements and in the rearrangement of the periodic table.
Cyclotrons can also be used to create isotopes — atoms of an element with the same number of protons but different numbers of neutrons packed into their nuclei — that can be used for medical treatments and imaging and for other research purposes. As an example, technetium-99, which was created with Berkeley’s 37-inch cyclotron and discovered by Carlo Perrier and Emilio Segrè, is used for millions of medical imaging scans a year worldwide.
As progressively larger cyclotrons outgrew Lawrence’s labs on the UC Berkeley campus, he moved to what is now Berkeley Lab’s home on an adjacent hillside. The first facility built on the new site was a massive 184-inch cyclotron. Its iconic dome, designed by famed San Francisco architect Arthur Brown Jr., now houses another accelerator: the Advanced Light Source.
Even as the cyclotron matured, Berkeley Lab scientists led the design and development of new concepts. Edwin McMillan was one of two independent discoverers of an important principle in particle acceleration called phase stability. The initial plans for the 184-Inch were revamped into a “synchro-cyclotron” that used this principle, transcending energy limits of the cyclotron.
McMillan then parlayed this principle into a ring-shaped electron accelerator, which he dubbed the “synchrotron.” Within just a few years, construction began on an ambitious synchrotron, called the Bevatron for its 6 billion electron volts (BeV) of energy, that reigned for several years as the most powerful in the world.
The Bevatron enabled the Nobel Prize-winning discovery of the antiproton, and two other Nobel Prizes were awarded based on research conducted at the Bevatron. Today, accelerators ranging from small medical synchrotrons to CERN’s Large Hadron Collider use this principle.
Berkeley Lab scientists have also driven many innovations in linear accelerators, which accelerate particles along a straight path and offer some different capabilities compared to ring-shaped accelerators.
Using a linear accelerator called the HILAC (and then its upgrade, the SuperHILAC) to accelerate heavy charged particles (ions), scientists added several more new elements to the periodic table. The eventual use of the SuperHILAC to produce beams of charged particles for further acceleration in the Bevatron — a combination dubbed the Bevalac — gave rise to the study of nuclear matter at extreme temperatures and pressures.
Lab accelerators also launched pioneering programs in biomedical research, including the use of accelerator-beam-based cancer therapies and the production of medical isotopes. Lawrence’s brother John, a medical doctor, was a pioneer in this early nuclear medicine research, which spawned new pathways in medical treatments that have since developed into well-established fields.
Since the beginning, Berkeley Lab has not only innovated in accelerator technology, but put beam on target for both intramural and visiting users. An example is the 88-Inch Cyclotron, a facility for cutting-edge nuclear science, including heavy-element research, as well as tests that show how electronic components stand up to the effects of simulated space radiation.
Staff at the 88-Inch Cyclotron have also played a central role in the development of ion sources that achieve high-charge states. A new Ion Source Group at the Lab works on the machines that create beams driving this field of research.
Accelerators that produce light
It was found early on that as electron beams bend in a synchrotron’s magnetic field, they give off light with such special and useful qualities that specialized accelerators were built just for this purpose. Berkeley Lab’s Advanced Light Source (ALS), launched in 1993, was among the first of a highly optimized new generation of these synchrotron light sources. Thousands of researchers each year come to the Lab to use the intense, focused beams of X-rays that the ALS provides.
In addition to Berkeley Lab’s accelerator design expertise, the ALS was made possible by the work of Berkeley Lab scientist and engineer Klaus Halbach, who pioneered the use of permanent-magnet arrays that wring laserlike x-ray beams out of the electron beam, as well as by the photon-beam-handling innovations of the Center for X-Ray Optics.
Light that produces acceleration
Light can also be used as a driver to accelerate particles. The Berkeley Lab Laser Accelerator (BELLA) Center features high-power laser systems that support an intense R&D effort in laser plasma acceleration. This technique accelerates electrons over a much shorter distance than is possible with conventional technology.
The BELLA petawatt laser enables research toward the high energies required for a next-generation particle collider while reducing the size and cost of such a machine compared to those of conventional large-scale accelerators. In a central research thrust enabled by the BELLA petawatt laser, achieving higher energies per acceleration stage, and learning more about how to use the output of one stage as the input to another, is a principal focus of BELLA Center. This system recently set a record, producing a beam with 8 GeV of energy in just 20 cm, a level of compact performance that conventional technology could not reach. The ultimate goal is a next-generation particle collider that provides beams relevant to high-energy physics in a package much smaller in size and cost than today’s.
Using a pair of hundred-terawatt laser systems, BELLA Center researchers are also pursuing multiple spinoff applications of their laser-driven acceleration technologies. Accelerators on a scale of centimeters, rather than tens of meters, could bring ALS-like synchrotron-light beams to a laboratory scale. Scattering of a second laser against the electron beam can create high-energy X-rays that can improve the effectiveness of imaging and characterization across a range of applications in security, medicine, and industry. Bending the electrons in a undulating motion using a series of magnets can create a brilliant source of softer X-rays useful for materials and bioscience. Ion acceleration is also being actively developed. These developments could bring the power now available only at large central facilities into the everyday life of more scientists as well as to an array of practical applications.
Laser innovation goes hand in hand with laser-plasma accelerator development. Lab researchers are working to develop an enabling technology for this progress: powerful and compact laser systems that fire thousands of times per second.
Innovating locally, accelerating globally
As accelerators became large, complex machines that required innovations and expertise from many disciplines, Lawrence and his lab championed a “team science” approach to realize their vision. Today the world’s most powerful accelerators and colliders require large teams of scientists, engineers, technicians, and others that can number into the thousands. Team science proved to be an innovation as powerful as the accelerators themselves: the heart of the unique capabilities of the national-laboratory system, it has also been embraced and applied to other fields by the worldwide scientific community.
In addition to Berkeley Lab’s own accelerators, its scientists and engineers have been instrumental in the design and construction of accelerators and their components for projects across the U.S. and internationally. Accelerator R&D and experiments here — and Lab scientists’ participation in experiments at other sites — have enabled discoveries of many subatomic particles and their properties, including the Higgs boson.
To take just a few recent examples, Berkeley Lab researchers are building powerful superconducting magnets for an upgrade of CERN’s Large Hadron Collider in Europe, which is the world’s largest particle collider, as just one example. They are also contributing an ion beam source magnet for the Facility for Rare Isotope Beams (FRIB) under construction at Michigan State University, and they designed and are now overseeing the construction and delivery of major components for an upgrade of the Linac Coherent Light Source X-ray laser at SLAC National Accelerator Laboratory in Menlo Park, California.
Computer modeling and simulation has been as transformative to accelerator R&D as to the rest of the technological world, and Berkeley Lab is a leader in the techniques of this field. An understanding of fundamental beam physics combines with Berkeley Lab computing resources to further the swift and accurate modeling and simulation of particle beams, and we are now using “virtual accelerators” to better understand, efficiently optimize and predict beam behavior.
The Lab has rich experience in developing accelerator controls and instrumentation as well, and applies it to projects worldwide.
Even as the biggest and most powerful accelerators make the headlines, Berkeley Lab advances new frontiers in small machines that can bring the accelerator to the application. The laser-plasma acceleration technology of BELLA is an example, applicable at a wide variety of scales and in many fields, from a field-portable cargo inspection system for nuclear security down to a cancer-treatment accelerator that we hope might someday apply beams directly at the site of a tumor. Another exciting innovation, newly patented after proof-of-concept R&D that joined us with Cornell University, is a compact and scalable multiple-beam accelerator based on inexpensive MEMS (micro-electro-mechanical systems) technology.
“We are thrilled to contribute to this continuing wave of innovation and progress that is ‘accelerating the future,’” said Thomas Schenkel, interim director of the Accelerator Technology and Applied Physics Division at Berkeley Lab. “From the beginning, accelerators have been transformative tools of discovery science and also building-blocks of innovation in technology and industry. The rich history of excellence in accelerator technologies here is the foundation upon which we are building the next generation of these tools.”